Two-dimensional (2D) scan engines are used in products such as retail store scanners to translate a target image (e.g., a barcode) into a digital format that can be interpreted and analyzed by a computer. Scan engines typically include an illumination system, a plurality of imaging pixel arrays (such as charge coupled device (CCD) or CMOS arrays), a lens, a sensor, and a decoder. In general, a scan engine scans the black and white elements of a target image (e.g., a barcode) by the illumination system illuminating the image with a light that passes through a transparent exit window and onto the target image. Light reflected from the target image typically is focused back through the exit window and through the lens, located on or near the scan engine, such that the focused light is concentrated onto one or more of the pixel arrays. The sensor detects the reflected light and generates an analog signal that is sent to the decoder. The decoder interprets that signal, validates the image, and converts it into text which may be delivered by the scan engine to a computer system holding a database of information against which the text may be compared.
In some situations, it is desirable to have the exit window positioned relatively close to the scan engine, for instance, to avoid reflections to the imaging pixel arrays which can distort the received image information. For instance, in some situations, it is desirable to have less than or equal to one millimeter of separation between the window and the scan engine. In such cases, however, it is not desirable to fix the positioning of the exit window as it is typically done in scanning devices having greater separation between the exit window and the scan engine. That is, it is not desirable to fix the positioning of the exit window to a rigid support structure using glue, bi-adhesive tape, ultrasonic welding, or the like, or to rigidly couple the exit window to the device enclosure. In the case of too weak tolerances of the parts of the scanning device assembly, such traditional means of fixing the exit window may make the assembly un-mountable. Further, the closeness of the exit window and the scan engine could transmit shocks in the case of mechanical stresses such as upon dropping of the scanning device.
These cases may be managed by a precise assembly having rigid assembly parts which are able to maintain constant the distance between the exit window and the scan engine while avoiding collision of these parts in the case of mechanical shocks.